Feasibility study into the measurement of stress upon the musculoskeletal system during the pushing and pulling of large refuse bins

Status:

completed 08/2011

Aims:

Owing to the work load of their refuse-collection tasks, refuse workers are among the workers in the waste management industry subject to major stresses upon their health. The full refuse bins are transported from the kerbside to the refuse vehicle, emptied there, and returned to the kerbside. The German Social Accident Insurance Institution for the transport industry has insufficient information on the stresses upon the musculoskeletal system caused by the pushing and pulling of refuse bins.
A feasibility study was therefore first to be conducted in order to develop methods for recording and measuring the physical stresses associated with the pushing and pulling of refuse bins. The external forces acting upon the musculoskeletal system were then to be determined under standardized conditions, and the stress factors quantified.

Activities/Methods:

The German Social Accident Insurance Institution for the transport industry provided three typical refuse bins of different volume and design. Hand force dynamometers developed at the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA) were then fitted to these bins for the purpose of measuring 3D hand forces. The CUELA system was used to record the body postures, joint angles of the upper and lower extremities and back posture, and the floor-reaction forces. Typical pushing, pulling and manoeuvring operations were studied on three different refuse bins (with capacities of 120, 240 and 1100 litres) and ten refuse workers. Pushing and pulling were performed on a test track. Asphalt was selected as the ground surface. The test track consisted of one longer (15 m) and one shorter (8 m) straight, interrupted by an obstacle course (15 m) for determining of the manoeuvring tasks. The test track also included a downward incline, an upward incline and a kerb. The refuse bins were weighted to different degrees. The loaded weights of the refuse bins had been determined previously in a field study conducted by the German Social Accident Insurance Institution for the transport industry. Manoeuvring of the refuse bins and the speed with which they were moved was left to the discretion of the refuse workers. The arrangement enabled at least 204 stress intervals per refuse worker to be recorded. The external stress data (body forces and angles) were to be interpreted by means of descriptive statistics.

Results:

The test arrangement described here was shown to be suitable for measuring the external forces acting upon the refuse workers and representing the stresses. The body postures, forces, directions of the forces, and finally the resulting external moments in the region of the lumbar spine were determined. The results show that the dynamic influence of the forces has a significant bearing upon the result. The average action forces during pushing and pulling lie between 32 N (sustained force on a half-full, 120 l refuse bin, pushing on the downward gradient) and 357 N (initial force on a full, 1100 l refuse bin, pushing on the obstacle course). The refuse workers confirmed that the test conditions cover the greater part of their normal work. The measured forces can therefore be used as a realistic basis for stress analysis of the refuse workers during kerbside refuse collection tasks.
Overall, the upper body postures of the refuse workers were not critical. The most favourable values here were measured with the 240 l refuse bins. The smaller 120 l bins and the heavy 1100 l bins force the refuse workers to adopt less favourable upper body postures.
In addition, the data recorded enable the moments arising in the region of the lumbar spine to be calculated from the forces and the upper body postures. Peak values are reached during the pushing of 120 l refuse bins and the pulling of 1100 l bins, in both cases full.
The following recommendations for the stress associated with kerbside refuse collection can be derived from these results:
1. A higher handle height or larger refuse bins contribute to a better body posture and reduce the action forces at a given bin load.
2. Heavy four-wheel refuse bins should be handled by pairs of workers in order for excessive stress to be avoided.

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